Speaking from the East Room of the White House, Obama said he had asked congressional leaders to postpone a vote on legislation he has been seeking to authorize the use of military force against Syria.

In a series of interviews on the Sunday news shows, Secretary of State John Kerry said the case for intervention in Syria’s 2 1/2-year civil war was strengthening each day and that he expected American lawmakers to recognize the need for action when the “credibility of the United States is on the line.”

The purpose of the study is to determine the best course of action in the event chemical, biological or radiological materials are released in the city, whether intentionally or not. The research will help officials decide on evacuation or sheltering plans.